The microstructure and dry sliding wear behav- ior of cast Al-18 wt% MgaSi in-situ metal matrix com- posite modified by Nd were investigated. Experimental results show that, after introducing a proper amount of Nd, bo...The microstructure and dry sliding wear behav- ior of cast Al-18 wt% MgaSi in-situ metal matrix com- posite modified by Nd were investigated. Experimental results show that, after introducing a proper amount of Nd, both primary and eutectic Mg2Si in the Al-18 wt% Mg2Si composite are well modified. The morphology of primary Mg2Si is changed from irregular or dendritic to polyhedral shape, and its average particle size is signifi- cantly decreased. Moreover, the morphology of the eutectic MgzSi phase is altered from flake-like to very short fibrous or dot-like. The wear rates and friction coefficient of the composites with Nd are lower than those without Nd. Furthermore, the addition of 0.5 wt% Nd changes the wear mechanism of the composite from the combination of abrasive, adhesive, and delamination wear without Nd into a single mild abrasion wear with 0.5 wt% Nd.展开更多
In the present study, the effects of mold temperature, superheat, mold thickness, and Mg_2Si amount on the fluidity of the Al-Mg_2Si as-cast in-situ composites were investigated using the mathematical models. Composit...In the present study, the effects of mold temperature, superheat, mold thickness, and Mg_2Si amount on the fluidity of the Al-Mg_2Si as-cast in-situ composites were investigated using the mathematical models. Composites with different amounts of Mg_2Si were fabricated, and the fluidity and microstructure of each were then analyzed. For this purpose, the experiments were designed using a central composite rotatable design, and the relationship between parameters and fluidity were developed using the response surface method. In addition, optical and scanning electron microscopes were used for microstructural observation. The ANOVA shows that the mathematical models can predict the fluidity accurately. The results show that by increasing the mold temperature from 25℃ to 200℃, superheat from 50℃ to 250℃, and thickness from 3 mm to 12 mm, the fluidity of the composites decreases, where the mold thickness is more effective than other factors. In addition, the higher amounts of Mg_2Si in the range from 15 wt.% to 25 wt.% lead to the lower fluidity of the composites. For example, when the mold temperature, superheat, and thickness are respectively 100℃, 150℃, and 7 mm, the fluidity length is changed in the range of 11.9 cm to 15.3 cm. By increasing the amount of Mg_2Si, the morphology of the primary Mg_2Si becomes irregular and the size of primary Mg_2Si is increased. Moreover, the change of solidification mode from skin to pasty mode is the most noticeable microstructural effect on the fluidity.展开更多
The semi-solid processed Mg2Si/A356 composites were fabricated using a sloping plate,and the phase and morphology evolution of the semi-solid Mg2Si/A356 slurry during the remelting process was investigated.Results ind...The semi-solid processed Mg2Si/A356 composites were fabricated using a sloping plate,and the phase and morphology evolution of the semi-solid Mg2Si/A356 slurry during the remelting process was investigated.Results indicate that compared to as-cast microstructure,the size of primaryα-Al phase and Mg2Si phase of semi-solid microstructure fabricated by using a sloping plate decreases and the morphology ofα-Al phase becomes fine and globular.With increasing the reheating temperature and prolonging the holding time,the primaryα-Al phase spheroidizes,the liquid fraction in semi-solid microstructure increases,and the Chinese script Mg2Si phase embedded in the primaryα-Al phase cannot be observed.The Chinese script Mg2Si phase is distributed in the secondaryα-Al phase and becomes smaller.The net-shaped eutectic phase also becomes finer after reheating.The optimum remelting parameters suitable for thixoforming in this study are remelting at 580℃for 30 min.展开更多
In the present study, by adding SiC particles into Al-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced Al matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex sit...In the present study, by adding SiC particles into Al-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced Al matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex situ stir casting. The as-cast microstructure containing primary Mg2Si and SiC particles that distribute homogenously in Al matrix was successfully achieved. The effects of SiC particle addition on the microstructure of Mg2Si/Al composites were investigated by using scanning electron microscopy(SEM) and XRD. The results show that, with increasing the fraction of the SiC particles from 5wt.% to 10wt.%, the morphologies of the primary Mg2Si particulates in the prepared samples remain polygonal, but the size of the primary phase decreases slightly. However, when the SiC particle addition reaches 15wt.%, the morphologies of the primary Mg2Si particulates change partially from polygonal to quadrangular with a decrease in size from 50 μm to 30 μm. The size of primary Al dendrites decreases with increasing fraction of the SiC particles from 0wt.% to 15wt.%. The morphology of the eutectic Mg2Si phase changes from a fi ber-form to a short fi ber-form and/or a dot-like shape with increasing fraction of the SiC particles. Furthermore, no signifi cant change in dendrite arm spacing(DAS) was observed in the presence of SiC particles.展开更多
To control the morphology and size of the primary and eutectic Mg2Si phases in in situ Mg2Si/Al-Si composite and achieve a feasible and reliable technique to produce appropriate feedstock for the thixo-casting and rhe...To control the morphology and size of the primary and eutectic Mg2Si phases in in situ Mg2Si/Al-Si composite and achieve a feasible and reliable technique to produce appropriate feedstock for the thixo-casting and rheo-casting of this type of material,three Al-Si matrix composites reinforced by 5wt.%,9wt.%and 17wt.%Mg2Si with hypoeutectic,eutectic and hypereutectic compositions were prepared by the low superheat pouring(LSP)process.The effects of the pouring temperature(superheat)on the morphology and size distribution of primary phases(primaryα-Al and Mg2Si),binary(α-Al+Mg2Si)eutectic cell and eutectic Mg2Si were investigated.The experimental results show that low pouring temperature(superheat)not only refines the grain structure of the primaryα-Al and binary(α-Al+Mg2Si)eutectic cell in three composites and promotes the formation of more nondendritic structural semi-solid metal(SSM)slurry of these phases;but also refines the primary and eutectic Mg2Si phases,which seems to be attributed to the creation of an ideal condition for the nucleation and the acquisition of a high survival of nuclei caused by the LSP process.展开更多
In this paper,the effect of the Si content on microstructure evolution,mechanical properties,and fracture behavior of the Al-xSi/AZ91D bimetallic composites prepared by compound casting was investigated systematically...In this paper,the effect of the Si content on microstructure evolution,mechanical properties,and fracture behavior of the Al-xSi/AZ91D bimetallic composites prepared by compound casting was investigated systematically.The obtained results showed that all the Al-xSi/AZ91D bimetallic composites had a metallurgical reaction layer(MRL),whose thickness increased with increasing Si content for the hypoeutectic Al-Si/AZ91D composites,while the hypereutectic Al-Si/AZ91D composites were opposite.The MRL included eutectic layer(E layer),intermetallic compound layer(IMC layer)and transition region layer(T layer).In the IMC layer,the hypereutectic Al-Si/AZ91D composites contained some Si solid solution and flocculent Mg_(2)Si+Al-Mg IMCs phases not presented in the hypoeutectic Al-Si/AZ91D composites.Besides,increasing Si content,the thickness proportion of the T layer increased,forming an inconsistent preferred orientation of the MRL.The shear strengths of the Al-xSi/AZ91D bimetallic composites enhanced with increasing Si content,and the Al-15Si/AZ91D composite obtained a maximum shear strength of 58.6 MPa,which was 73.4% higher than the Al-6Si/AZ91D composite.The fractures of the Al-xSi/AZ91D bimetallic composites transformed from the T layer into the E layer with the increase of the Si content.The improvement of the shear strength of the Al-xSi/AZ91D bimetallic composites was attributed to the synergistic action of the Mg_(2)Si particle reinforcement,the reduction of oxidizing inclusions and the ratio of Al-Mg IMCs as well as the orientation change of the MRL.展开更多
The effect of Mg_(2)Si amount on the properties of Al-Mg_(2)Si as-cast composites was investigated in this study.Composites with different amounts of Mg_(2)Si(15 wt%,20 wt%and 25 wt%)were fabricated,and the fluidity,v...The effect of Mg_(2)Si amount on the properties of Al-Mg_(2)Si as-cast composites was investigated in this study.Composites with different amounts of Mg_(2)Si(15 wt%,20 wt%and 25 wt%)were fabricated,and the fluidity,viscosity,porosity formation and tensile properties were then analyzed.In addition,optical microscope and scanning electron microscope were used for micros tructural studies and fractography.The results reveal that with the amount of Mg_(2)Si increasing,the morphology of the primary Mg_(2)Si becomes irregular,the size of primary Mg_(2)Si increases,fluidity decreases,viscosity increases,and porosity amount increases.The reason for the higher amounts of porosities is the lower fluidity and higher viscosity.In addition,Al-15%Mg_(2)Si shows better tensile properties and higher quality index compared to other composites.Furthermore,the fracture surface of the composite with lower Mg_(2)Si amount reveals more ductile mode than those with higher Mg_(2)Si amount.展开更多
The influence of Nd on the microstructures, tensile properties and fracture behavior of cast Al-18 wt.%Mg2Si/n situ metal matrix composite was investigated. Experimental results showed that, after introducing a proper...The influence of Nd on the microstructures, tensile properties and fracture behavior of cast Al-18 wt.%Mg2Si/n situ metal matrix composite was investigated. Experimental results showed that, after introducing a proper amount of Nd, both primary and eutectic Mg2Si in the Al-18 wt.%Mg2Si composite were well modified. The morphology of primary MgaSi was changed fi＇om irregular or dendritic to polyhedral shape, and its average particle size was significantly decreased from 47.5 to 13.0 μm. Moreover, the morphology of the eutectic Mg2Si phase was altered from flake-like to a thin laminar, short fibrous or dot-like structure. Tensile tests revealed that Nd addition improved the tensile strength and ductility of the material. Compared with those of unmodified composite, the ultimate tensile strength and percentage elongation with 0.5% Nd were increased by 32.4% and 200%, respectively. At the same time, Nd addition changed the fracture behavior from brittle to ductile.展开更多
基金financially supported by the National Natural Youth Science Foundation of China (No. 50901038)the Key Laboratory Foundation of Liaoning Provincial Committee of Education (Nos. 20060394 and 2009S053)
文摘The microstructure and dry sliding wear behav- ior of cast Al-18 wt% MgaSi in-situ metal matrix com- posite modified by Nd were investigated. Experimental results show that, after introducing a proper amount of Nd, both primary and eutectic Mg2Si in the Al-18 wt% Mg2Si composite are well modified. The morphology of primary Mg2Si is changed from irregular or dendritic to polyhedral shape, and its average particle size is signifi- cantly decreased. Moreover, the morphology of the eutectic MgzSi phase is altered from flake-like to very short fibrous or dot-like. The wear rates and friction coefficient of the composites with Nd are lower than those without Nd. Furthermore, the addition of 0.5 wt% Nd changes the wear mechanism of the composite from the combination of abrasive, adhesive, and delamination wear without Nd into a single mild abrasion wear with 0.5 wt% Nd.
文摘In the present study, the effects of mold temperature, superheat, mold thickness, and Mg_2Si amount on the fluidity of the Al-Mg_2Si as-cast in-situ composites were investigated using the mathematical models. Composites with different amounts of Mg_2Si were fabricated, and the fluidity and microstructure of each were then analyzed. For this purpose, the experiments were designed using a central composite rotatable design, and the relationship between parameters and fluidity were developed using the response surface method. In addition, optical and scanning electron microscopes were used for microstructural observation. The ANOVA shows that the mathematical models can predict the fluidity accurately. The results show that by increasing the mold temperature from 25℃ to 200℃, superheat from 50℃ to 250℃, and thickness from 3 mm to 12 mm, the fluidity of the composites decreases, where the mold thickness is more effective than other factors. In addition, the higher amounts of Mg_2Si in the range from 15 wt.% to 25 wt.% lead to the lower fluidity of the composites. For example, when the mold temperature, superheat, and thickness are respectively 100℃, 150℃, and 7 mm, the fluidity length is changed in the range of 11.9 cm to 15.3 cm. By increasing the amount of Mg_2Si, the morphology of the primary Mg_2Si becomes irregular and the size of primary Mg_2Si is increased. Moreover, the change of solidification mode from skin to pasty mode is the most noticeable microstructural effect on the fluidity.
基金the National Natural Science Foundation of China(Grant No.51865011)the Natural Science Foundation of Jiangxi Province,China(Grant No.20171BAB216031).
文摘The semi-solid processed Mg2Si/A356 composites were fabricated using a sloping plate,and the phase and morphology evolution of the semi-solid Mg2Si/A356 slurry during the remelting process was investigated.Results indicate that compared to as-cast microstructure,the size of primaryα-Al phase and Mg2Si phase of semi-solid microstructure fabricated by using a sloping plate decreases and the morphology ofα-Al phase becomes fine and globular.With increasing the reheating temperature and prolonging the holding time,the primaryα-Al phase spheroidizes,the liquid fraction in semi-solid microstructure increases,and the Chinese script Mg2Si phase embedded in the primaryα-Al phase cannot be observed.The Chinese script Mg2Si phase is distributed in the secondaryα-Al phase and becomes smaller.The net-shaped eutectic phase also becomes finer after reheating.The optimum remelting parameters suitable for thixoforming in this study are remelting at 580℃for 30 min.
基金supported by the National Natural Science Foundation of China(No.50671044)the Sci-tech Development Project of Jilin Province of China(No.20070506)
文摘In the present study, by adding SiC particles into Al-Si-Mg melt, Mg2Si and SiC particles hybrid reinforced Al matrix composites were fabricated through the Mg2Si in situ synthesis in melt combined with the SiC ex situ stir casting. The as-cast microstructure containing primary Mg2Si and SiC particles that distribute homogenously in Al matrix was successfully achieved. The effects of SiC particle addition on the microstructure of Mg2Si/Al composites were investigated by using scanning electron microscopy(SEM) and XRD. The results show that, with increasing the fraction of the SiC particles from 5wt.% to 10wt.%, the morphologies of the primary Mg2Si particulates in the prepared samples remain polygonal, but the size of the primary phase decreases slightly. However, when the SiC particle addition reaches 15wt.%, the morphologies of the primary Mg2Si particulates change partially from polygonal to quadrangular with a decrease in size from 50 μm to 30 μm. The size of primary Al dendrites decreases with increasing fraction of the SiC particles from 0wt.% to 15wt.%. The morphology of the eutectic Mg2Si phase changes from a fi ber-form to a short fi ber-form and/or a dot-like shape with increasing fraction of the SiC particles. Furthermore, no signifi cant change in dendrite arm spacing(DAS) was observed in the presence of SiC particles.
文摘To control the morphology and size of the primary and eutectic Mg2Si phases in in situ Mg2Si/Al-Si composite and achieve a feasible and reliable technique to produce appropriate feedstock for the thixo-casting and rheo-casting of this type of material,three Al-Si matrix composites reinforced by 5wt.%,9wt.%and 17wt.%Mg2Si with hypoeutectic,eutectic and hypereutectic compositions were prepared by the low superheat pouring(LSP)process.The effects of the pouring temperature(superheat)on the morphology and size distribution of primary phases(primaryα-Al and Mg2Si),binary(α-Al+Mg2Si)eutectic cell and eutectic Mg2Si were investigated.The experimental results show that low pouring temperature(superheat)not only refines the grain structure of the primaryα-Al and binary(α-Al+Mg2Si)eutectic cell in three composites and promotes the formation of more nondendritic structural semi-solid metal(SSM)slurry of these phases;but also refines the primary and eutectic Mg2Si phases,which seems to be attributed to the creation of an ideal condition for the nucleation and the acquisition of a high survival of nuclei caused by the LSP process.
基金the supports provided by the National Natural Science Foundation of China(Nos.52075198 and 52271102)the China Postdoctoral Science Foundation(No.2021M691112)+1 种基金the State Key Lab of Advanced Metals and Materials(No.2021-ZD07)the Analytical and Testing Center,HUST。
文摘In this paper,the effect of the Si content on microstructure evolution,mechanical properties,and fracture behavior of the Al-xSi/AZ91D bimetallic composites prepared by compound casting was investigated systematically.The obtained results showed that all the Al-xSi/AZ91D bimetallic composites had a metallurgical reaction layer(MRL),whose thickness increased with increasing Si content for the hypoeutectic Al-Si/AZ91D composites,while the hypereutectic Al-Si/AZ91D composites were opposite.The MRL included eutectic layer(E layer),intermetallic compound layer(IMC layer)and transition region layer(T layer).In the IMC layer,the hypereutectic Al-Si/AZ91D composites contained some Si solid solution and flocculent Mg_(2)Si+Al-Mg IMCs phases not presented in the hypoeutectic Al-Si/AZ91D composites.Besides,increasing Si content,the thickness proportion of the T layer increased,forming an inconsistent preferred orientation of the MRL.The shear strengths of the Al-xSi/AZ91D bimetallic composites enhanced with increasing Si content,and the Al-15Si/AZ91D composite obtained a maximum shear strength of 58.6 MPa,which was 73.4% higher than the Al-6Si/AZ91D composite.The fractures of the Al-xSi/AZ91D bimetallic composites transformed from the T layer into the E layer with the increase of the Si content.The improvement of the shear strength of the Al-xSi/AZ91D bimetallic composites was attributed to the synergistic action of the Mg_(2)Si particle reinforcement,the reduction of oxidizing inclusions and the ratio of Al-Mg IMCs as well as the orientation change of the MRL.
文摘The effect of Mg_(2)Si amount on the properties of Al-Mg_(2)Si as-cast composites was investigated in this study.Composites with different amounts of Mg_(2)Si(15 wt%,20 wt%and 25 wt%)were fabricated,and the fluidity,viscosity,porosity formation and tensile properties were then analyzed.In addition,optical microscope and scanning electron microscope were used for micros tructural studies and fractography.The results reveal that with the amount of Mg_(2)Si increasing,the morphology of the primary Mg_(2)Si becomes irregular,the size of primary Mg_(2)Si increases,fluidity decreases,viscosity increases,and porosity amount increases.The reason for the higher amounts of porosities is the lower fluidity and higher viscosity.In addition,Al-15%Mg_(2)Si shows better tensile properties and higher quality index compared to other composites.Furthermore,the fracture surface of the composite with lower Mg_(2)Si amount reveals more ductile mode than those with higher Mg_(2)Si amount.
基金Project supported by Key Laboratory Foundation of Liaoning Provincial Committee of Education (2009S053)
文摘The influence of Nd on the microstructures, tensile properties and fracture behavior of cast Al-18 wt.%Mg2Si/n situ metal matrix composite was investigated. Experimental results showed that, after introducing a proper amount of Nd, both primary and eutectic Mg2Si in the Al-18 wt.%Mg2Si composite were well modified. The morphology of primary MgaSi was changed fi＇om irregular or dendritic to polyhedral shape, and its average particle size was significantly decreased from 47.5 to 13.0 μm. Moreover, the morphology of the eutectic Mg2Si phase was altered from flake-like to a thin laminar, short fibrous or dot-like structure. Tensile tests revealed that Nd addition improved the tensile strength and ductility of the material. Compared with those of unmodified composite, the ultimate tensile strength and percentage elongation with 0.5% Nd were increased by 32.4% and 200%, respectively. At the same time, Nd addition changed the fracture behavior from brittle to ductile.
